The first E20's AA ,BA,CA,DA used 4 solenoids and a shunt resistor to "measure" current for control purposes. All fine and dandy when oxidation and age aren't present. Another thing not taken into account was passing high current over bolt threads in manual cutoff switch, motor pass-thru bolts and other places- not good. Electricity likes very smooth surfaces. With time the shunt resistors became a real problem. The original smooth action units became jerky with burnt up shunt resistors. Later units used 2 solenoids and a "2AH" relay to sense low armature voltage instead. By the time engineers had figured out how to head off long term problems the advantages or allure of the E20 had passed. The amazing thing is how many are left to be restored to some form of "glory". I am not ready to go to solid state controller yet- magic smoke still makes my nose twinge way too much

For clarity my original post referred to the initial engagment process. On early E20's it took 5 solenoids engaged for full power to armature. The later took only 3 on for full forward power. Another reason I will stick with original wiring .